Dynamic resource allocation in packet data transfer

ABSTRACT

A method for control of packet data transmissions in a TDMA wireless network to provide for additional choices in the allocation of communication channels. Measurement and recovery periods are re-assigned to avoid conflicts in operating conditions. The re-assignments for the GPRS system may be reduced to a simple formula.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to multiple access communication systemsand in particular it relates to dynamic resource allocation in timedivision multiple access systems.

[0003] 2. Description of Related Art

[0004] In Multiple access wireless systems such as GSM, a number ofmobile stations communicate with a network. The allocation of physicalcommunication channels for use by the mobile stations is fixed. Adescription of the GSM system may be found in The GSM System for MobileCommunications by M. Mouly and M. B. Pautet, published 1992 with theISBN reference 2-9507190-0-7.

[0005] With the advent of packet data communications over Time DivisionMultiple Access (TDMA) systems, more flexibility is required in theallocation of resources and in particular in the use of physicalcommunication channels. For packet data transmissions in General PacketRadio Systems (GPRS) a number of Packet Data CHannels (PDCH) provide thephysical communication links. The time division is by frames of 4.615 msduration and each frame has eight consecutive 0.577 ms slots. Adescription of the GPRS system may be found in (GSM 03.64 V 8.5 release1999). The slots may be used for uplink or downlink communication.Uplink communication is a transmission from the mobile station forreception by the network to which it is attached. Reception by themobile station of a transmission from the network is described asdownlink.

[0006] In order to utilise most effectively the available bandwidth,access to channels can be allocated in response to changes in channelconditions, traffic loading Quality of service and subscription class.Owing to the continually changing channel conditions and trafficloadings a method for dynamic allocation of the available channels isavailable.

[0007] The amounts of time that the mobile station receives downlink ortransmits uplink may be varied and slots allocated accordingly. Thesequences of slots allocated for reception and transmission, theso-called multislot pattern is usually described in the form RXTY. Theallocated receive (R) slots being the number X and the allocatedtransmit slots (T) the number Y.

[0008] A number of multislot classes, one through to 29, is defined forGPRS operation and the maximum uplink (Tx) and downlink (Rx) slotallocations are specified for each class. The specification formultislot class 12 is shown in Table 1 below.

[0009] In a GPRS system, access to a shared channel is controlled bymeans of an Uplink Status Flag (USF) transmitted on the downlink to eachcommunicating mobile station (MS). In GPRS two allocation methods aredefined, which differ in the convention about which uplink slots aremade available on receipt of a USF. The present invention relates to aparticular allocation method, in which an equal number “N” of PDCH's,where a “PDCH” uses a pair of uplink and downlink slots corresponding toeach other on a 1-1 basis, are allocated for potential use by the MS.The uplink slots available for actual use by a particular mobile stationsharing the uplink channel are indicated in the USF. The USF is a dataitem capable of taking 8 values V0- V7, and allows uplink resources tobe allocated amongst up to 8 mobiles where each mobile recognises one ofthese 8 values as ‘valid’, i.e. conferring exclusive use of resources tothat mobile. In the case of the extended dynamic allocation method, forexample, reception of a valid USF in the slot 2 of the present framewill indicate the actual availability for transmission of transmit slots2 . . . N in the next TDMA frame or group of frames, where N is thenumber of allocated PDCHs. Generally for a valid USF received atreceiver slot n, transmission takes place in the next transmit frame attransmit slots n, n+1 et seq. to the allocated number of slots (N). Forthe extended dynamic allocation method as presently defined theseallocated slots are always consecutive.

[0010] The mobile station is not able instantly to switch from a receivecondition to a transmit condition or vice versa and the time allocatedto these reconfigurations is known as turnaround time. As presentlydefined the turnaround time depends upon the class of mobile. Aturnaround time of one slot is allocated in the case of class 12 mobilessuch as are used for the exemplary embodiment. It is also necessary forthe mobile station, whilst in packet transfer mode, to performneighbourhood cell measurements. The mobile station has continuously tomonitor all Broadcast Control Channel (BCCH) carriers as indicated bythe BA(GPRS) list and the BCCH carrier of the serving cell. A receivedsignal level measurement sample is taken in every TDMA frame, on atleast one of the BCCH carriers. (GSM 05.08 10.1.1.2)

[0011] These neighbour cell measurements are taken prior tore-configuration from reception to transmission or prior tore-configuration from transmission to reception. The number of slotsallocated to each of these measurements and re-configurations formultislot class 12 is two.

[0012] Arising from the requirement to allocate particular slots forturnaround and measurement purposes, some restrictions occur andpotential dynamic channel allocations are lost. These restrictionsreduce the availability of slots for uplink transmissions; reduce theflow of data and reduce the flexibility of response to changingconditions.

[0013] An exhaustive technical review and wholesale change to theexisting prescribed operating conditions might be expected to alleviatethe problems associated with dynamic allocation. Whilst this ispossible, the considerable difficulties caused by such wholesale changewould be generally unwelcome and this resolution of the technicalproblem is unlikely.

[0014] There is a need therefore to provide a solution to the problemsaffecting dynamic channel allocation with minimal effect on existingprior art methods.

SUMMARY OF THE INVENTION

[0015] It is an object of this invention to reduce the restrictionsaffecting dynamic channel allocation with minimal effect on the existingprescript.

[0016] In accordance with the invention there is provided a method forcontrolling packet data transmissions as set out in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] An embodiment of the invention will now be described withreference to the accompanying figures in which:

[0018]FIG. 1 illustrates the GPRS TDMA frame structure showing thenumbering convention used for uplink and downlink timeslots;

[0019]FIG. 2 illustrates a 3 slot allocation and a state transition fromR3T0 to R3T2;

[0020] FIGS. 3 to 6 show 2 PDCH extended dynamic allocations in steadystate for R2T0, R2T1 and R2T2 respectively with associated measurementand turnaround intervals;

[0021]FIG. 6 is a state transition diagram for 2 PDCH extended dynamicallocations;

[0022] FIGS. 7 to 11 show the state transitions of FIG. 6;

[0023]FIG. 12 to 15 show the 3 PDCH extended dynamic allocation insteady state;

[0024]FIG. 16 is a state transition diagram for 3 PDCH extended dynamicallocation;

[0025] FIGS. 17 to 25 show the state transitions of FIG. 16;

[0026] FIGS. 26 to 30 show the steady state 4 slot extended dynamicallocation of the prior art;

[0027] FIGS. 31 to 35 show the steady state 4 slot extended dynamicallocation in accordance with the invention;

[0028]FIG. 36 is a state transition diagram for 4 slot extended dynamicallocation in accordance with the invention; and

[0029] FIGS. 37 to 50 show the state transitions of FIG. 36.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In this embodiment, the invention is applied to a GPRS wirelessnetwork operating in accordance with the standards applicable tomultislot class 12.

[0031] In FIG. 1 the GPRS TDMA frame structure is illustrated and showsthe numbering convention used for uplink and downlink timeslots. Itshould be noted that in practice Tx may be advanced relative to Rx dueto timing advance, although this is not shown in the illustration. Thusin practice the amount of time between the first Rx and first Tx of aframe may be reduced a fraction of a slot from the illustrated value of3 slots due to timing advance. Two successive TDMA frames areillustrated with receiver (Rx) and transmitter (Tx) slots identifiedseparately. The slot positions within the first frame are shown by thenumerals 1 through to 8 with the transmission and reception slots offsetby a margin of three slots. This is in accordance with the conventionthat that the first transmit frame in a TDMA lags the first receiveframe by an offset of 3 (thus ordinary single slot GSM can be regardedas a particular case in which only slot 1 of transmit and receive isused).

[0032] The remaining figures (save for the state transition diagrams)conform to the illustration of FIG. 1 but the slot numbering has beenremoved for extra clarity. The shaded slots are those allocated for theparticular states and the arrowed inserts e.g. numerals 41 and 42 ofFIG. 4 indicate the applicable measurement and turnaround intervals andnumber of slots allocated for these intervals. The hashed slots e.g.numeral 43 of FIG. 4 indicate reception of a valid USF. As mentionedabove, constraints are imposed by the need to allow measurement andturnaround slots and the prescript for these in 05.02 Annex B limitsdynamic allocation as shown in table 1 for the example of multislotclass 12. TABLE 1 Multislot Maximum number of slots Minimum number ofslots class Rx Tx Sum T_(ta) T_(tb) T_(ra) T_(rb) 12 4 4 5 2 1 2 1

[0033] The measurement period for extended dynamic allocation isspecified (05.02 6.4.2.2) as Tra. That is to say that all neighbourmeasurements are taken just before the first receive slot and not beforethe transmit slot.

[0034] If there are m timeslots allocated for reception and n timeslotsallocated for transmission, then there must be Min(m,n) reception andtransmission timeslots with the same timeslot number.

[0035] With reference to FIG. 2, an example of a 3 slot allocation,annotated R3T0→R3T2, is shown with no uplink slot allocated initially. Avalid USF received on Rx slot 2 allows 2 TX slots on the next uplinkframe. The annotation → indicates a change of state.

[0036] The FIGS. 3 to 5 show steady state extended dynamic allocationsfor 2 PDCH according to the annotations and the measurement andturnaround intervals are marked. FIG. 6 is a state transition diagramfor 2 PDCH extended dynamic allocations and shows all of the allowedstates.

[0037] FIGS. 7 through to 11 show the slot positions and applicablemeasurement and turnaround intervals for the transitions of FIG. 6.

[0038] Steady state 3 PDCH extended dynamic allocations are shown inFIGS. 12 to 15. The state transitions for 3PDCH are shown in FIG. 16 andthe corresponding slot positions and measurement and turnaroundintervals in FIGS. 17 to 25. It can be seen that for all of theillustrations no impediment to slot allocation arises from theapplication of the measurement and turnaround intervals.

[0039] With 4 slot extended dynamic allocations, however conflicts occurand the prescribed conditions do not permit implementation beyond thesteady state R4T0 case illustrated in FIG. 26. This is because theconstraint T_(ra)=2 for neighbour cell measurement cannot be appliedsince Tx slot 4 is always used, leaving only a single slot turnaroundtime before Rx slot 1. Examples of allowed and prohibited 4 slotextended dynamic allocations in accordance with the prior art are shownin FIGS. 26 to 30. These indicate steady states and the four receiveslots and no transmit slot R4T0 state of FIG. 26 is allowed. Theallocations prohibited are overlaid by a “no entry” logo (e.g. numeral301 of FIG. 30) in the illustrations of FIG. 27, R4T1, FIG. 28, R3T2,FIG. 29 R2T3 and FIG. 30 R1T4. It can be seen that these prohibitionsarise because of the limitation of one slot allowed for the measurementand preparation Tra (the time needed to measure and then prepare fortransmission).

[0040] In accordance with the invention there is re-allocation ofmeasurement and recovery periods to increase the availability of uplinkresources when uplink resources are otherwise constrained by prescribedallocations.

[0041] Application of the method in accordance with the inventionprovides for the previously prohibited allocations of FIGS. 27 to 30 tobe admitted as shown in FIGS. 32 to 35. If N slots are allocated, andN+T_(ra)+3 <=8 (number of slots in a frame), then T_(ra) is used as themeasurement interval otherwise if N+T_(ra)+3 >8 . . . (XX), then T_(ta)is used as the measurement interval; where

[0042] <=less than or equal to

[0043] > greater than

[0044] T_(ta) is the time needed to measure and then prepare fortransmission

[0045] Application of the method to the steady state R4T1 is shown inFIG. 32,

[0046] With the number of PDCH's allocated N=4, the measurement andpreparation interval T_(ra)=2, N+T_(ra)+3>8 (4+2+3=9) therefore T_(ta)is used as the measurement interval. The impediment to operation shownin FIG. 27 is therefore removed by application of the method asillustrated in FIG. 32.

[0047] This procedure is implemented in the mobile station which whenusing the extended dynamic allocation method, and on receiving anallocation of PDCH numbering ‘N’, must perform the comparison above inorder to time the radio link measurement procedure correctly.

[0048] The procedure performed by the network equipment is that whenallocating a number of PDCHs ‘N’, it recognise that when N satisfies thecondition (XX) above it must take into account the capability of themobile station to perform measurements using T_(ta) and provided that:N+T_(rb)+3<=8, is capable of allocating such a number of PDCHs.

[0049] The method may be applied successfully to the remaining steadystates shown in FIGS. 33, 34 and 35. Furthermore the method is effectivefor all of the 4 slot state transitions shown in the state transitiondiagram FIG. 6. Illustrations of the 4 slot state transitions are givenin FIGS. 37 through to 50.

1-12. (Canceled).
 13. A communication method used in a mobile stationapparatus which performs communication using a reception TDMA frameformed by eight reception slots and a transmission TDMA frame formed byeight transmission slots, an offset between the reception TDMA frame andthe transmission TDMA frame being three slots, the method comprising thesteps of: performing preparation for reception; performing receptionusing the reception slot; performing preparation for transmission;performing transmission using the transmission slot; and performingadjacent cell signal level measurement together with either thepreparation for reception or the preparation for transmission, wherein(i) when a number of transmission slots used in one transmission frameis below a predetermined number, then the adjacent cell signal levelmeasurement and the preparation for reception are performed in a periodof two slots before a first reception slot and (ii) when the number oftransmission slots used in one transmission frame is the predeterminednumber, then the adjacent cell signal level measurement and thepreparation for transmission are performed in a period of two slotsbefore a first transmission slot.
 14. The method according to claim 13,wherein the predetermined number is four.
 15. The method according toclaim 13, wherein the method is applied to a multi-slot class 12 in aGeneral Packet Radio System (GPRS).
 16. A communication method used in amobile station apparatus which performs communication using a receptionTDMA frame formed by eight reception slots and a transmission TDMA frameformed by eight transmission slots, an offset between the reception TDMAframe and the transmission TDMA frame being three slots, the methodcomprising the steps of: performing preparation for reception;performing reception using the reception slot; performing preparationfor transmission; performing transmission using the transmission slot;and performing adjacent cell signal level measurement together witheither the preparation for reception or the preparation fortransmission, wherein when a number of transmission slots used in onetransmission frame is a predetermined number and when there is not atime of two slots necessary for the adjacent cell signal levelmeasurement and the preparation for reception after a last transmissionslot, then the adjacent cell signal level measurement and thepreparation for transmission are performed in a period of two slotsbefore a first transmission slot.
 17. The method according to claim 16,wherein the predetermined number is four.
 18. The method according toclaim 16, wherein the method is applied to a multi-slot class 12 in aGeneral Packet Radio System (GPRS).
 19. A communication method used in amobile station apparatus which performs communication using a receptionTDMA frame formed by a plurality of reception slots and a transmissionTDMA frame formed by a plurality of transmission slots, the methodcomprising the steps of: performing preparation for reception;performing reception using the reception slot; performing preparationfor transmission; performing transmission using the transmission slot;and performing adjacent cell signal level measurement together witheither the preparation for reception or the preparation fortransmission, wherein (i) only both when a number of transmission slotsused in one transmission frame is equal to or greater than apredetermined number and when there is no time for performing theadjacent cell signal level measurement and the preparation for receptionafter a last transmission slot, then the adjacent cell signal levelmeasurement is performed together with the preparation for transmissionand (ii) in other cases the adjacent cell signal level measurement isperformed together with the preparation for reception.
 20. The methodaccording to claim 19, wherein the predetermined number is four.
 21. Themethod according to claim 19, wherein the method is applied to amulti-slot class 12 in a General Packet Radio System (GPRS).
 22. Amobile station apparatus which performs communication using a receptionTDMA frame formed by eight reception slots and a transmission TDMA frameformed by eight transmission slots, an offset between the reception TDMAframe and the transmission TDMA frame being three slots, the apparatuscomprising: a reception preparation section that performs preparationfor reception; a reception section that performs reception using thereception slot; a transmission preparation section that performspreparation for transmission; a transmission section that performstransmission using the transmission slot; and a measurement section thatperforms adjacent cell signal level measurement together with either thepreparation for reception or the preparation for transmission, wherein(i) when a number of transmission slots used in one transmission frameis below a predetermined number, then the adjacent cell signal levelmeasurement and the preparation for reception are performed in a periodof two slots before a first reception slot and (ii) when the number oftransmission slots used in one transmission frame is the predeterminednumber, then the adjacent cell signal level measurement and thepreparation for transmission are performed in a period of two slotsbefore a first transmission slot.
 23. The apparatus according to claim22, wherein the predetermined number is four.
 24. The apparatusaccording to claim 22, wherein the method is applied to a multi-slotclass 12 in a General Packet Radio System (GPRS).